Showing papers by "Klaus Werner Stöckelhuber published in 2004"
TL;DR: Experimental data of rupture thickness and lifetime of wetting films of pure electrolyte and surfactant solutions show that the stabilization of the foam film by surfactants has a crucial effect on the stability of the wetting film.
Abstract: It is now widely accepted that nanometer sized bubbles, attached at a hydrophobic silica surface, can cause rupture of aqueous wetting films due to the so-called nucleation mechanism. But the knowledge of the existence of such nanobubbles does not give an answer to how the subprocesses of this rupture mechanism operate. The aim of this paper is to describe the steps of the rupture process in detail: (1) During drainage of the wetting film, the apex of the largest nanobubble comes to a distance from the wetting film surface, where surface forces are acting. (2) An aqueous "foam film" in nanoscale size is formed between the bubble and the wetting film surface; in this foam film different Derjaguin-Landau-Verwey-Overbeek (DLVO) forces are acting than in the surrounding wetting film. In the investigated system, hydrophobized silica/water/air, all DLVO forces in the wetting film are repulsive, whereas in the foam film the van der Waals force becomes attractive. (3) The surface forces over and around the apex of the nanobubble lead to a deformation of the film surfaces, which causes an additional capillary pressure in the foam film. An analysis of the pressure balance in the system shows that this additional capillary pressure can destabilize the foam film and leads to rupture of the foam film. (4) If the newly formed hole in the wetting film has a sufficient diameter, the whole wetting film is destabilized and the solid becomes dewetted. Experimental data of rupture thickness and lifetime of wetting films of pure electrolyte and surfactant solutions show that the stabilization of the foam film by surfactants has a crucial effect on the stability of the wetting film.
107 citations
TL;DR: In this article, the stability of TiO2 suspensions in photocatalytic reactors for degradation of pollutants is described as a result of competition between the electrostatic repulsion and the attraction due to the van der Waals and hydrophobic interactions.
Abstract: The stability of TiO2 suspensions in photocatalytic reactors for degradation of pollutants is described as a result of competition between the electrostatic repulsion and the attraction due to the van der Waals and hydrophobic interactions. A simple expression for the hydrophobic force is derived, which depends substantially on the pollutant concentration and the adsorption length. The stability analysis performed yields a power dependence of the critical pollutant concentration on the electrolyte concentration, above which the suspensions are unstable. The scaling parameters of this power law depend significantly on the adsorption length and they are tabulated in the paper.
1 citations